Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$90.98	3.486%	$94.1516	$94.15	$94.15	$94.20
Purchase #2	$86.82	5.179%	$91.3164	$91.32	$91.30	$91.30
Purchase #3	$140.88	4.520%	$147.2478	$147.25	$147.25	$147.20
Purchase #4	$153.26	5.473%	$161.6479	$161.65	$161.65	$161.60
Purchase #5	$71.57	8.856%	$77.9082	$77.91	$77.90	$77.90
Purchase #6	$144.38	9.463%	$158.0427	$158.04	$158.05	$158.00
Purchase #7	$107.51	3.501%	$111.2739	$111.27	$111.25	$111.30
7 purchase totals =	$795.40		$841.5885	$841.59	$841.55	$841.50